1. Field of the Invention
The invention relates to a thin film magnetic head comprising at least an inductive magnetic transducer for writing and a method of manufacturing the same.
2. Description of the Related Art
In recent years, performance improvement in thin film magnetic heads has been sought in accordance with an increase in surface recording density of a hard disk drive. As a thin film magnetic head, a composite thin film magnetic head has been widely used. A composite thin film magnetic head has a layered structure which includes a recording head with an inductive magnetic transducer for writing and a reproducing head with a magnetoresistive device (referred to as MR device in the followings) for reading-out. There are a few types of MR devices: one is an AMR device that utilizes an anisotropic magnetoresistive effect (referred to as AMR effect in the followings) and the other is a GMR device that utilizes a giant magnetoresistive effect (referred to as GMR effect in the followings). A reproducing head using the AMR device is called an AMR head or simply an MR head. A reproducing head using the GMR device is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is more than 1 gigabit per square inch. The GMR head is used as a reproducing head whose surface recording density is more than 3 gigabits per square inch.
The AMR head includes an AMR film having the AMR effect. The GMR head has the similar configuration to the AMR head except that the AMR film is replaced with a GMR film having the GMR effect. However, compared to the AMR film, the GMR film exhibits a greater change in resistance under a specific external magnetic field. Accordingly, the reproducing output of the GMR head becomes about three to five times greater than that of the AMR head.
In order to improve the performance of a reproducing head, the MR film may be changed from an AMR film to a GMR film or the like which is made of a material with more excellent magnetoresistive sensitivity. The pattern width of the MR film, specifically the MR height, may be adjusted appropriate. The MR height is the length (height) between the edge of an MR element closer to an air bearing surface and the other edge, and is determined by an amount of polishing the air bearing surface. The air bearing surface (ABS) is a surface of a thin film magnetic head facing a magnetic recording medium and is also called a track surface.
Performance improvement in a recording head has also been expected in accordance with the performance improvement in a reproducing head. The main factor which determines the performance of a recording head is a throat height (TH). The throat height is a length (height) of a portion of a magnetic pole from the air bearing surface to an edge of an insulating layer which electrically isolates a thin film coil for generating a magnetic flux. It is necessary to reduce the throat height in order to improve the performance of the recording head. The throat height is also controlled by an amount of polishing the air bearing surface.
It is necessary to increase the track density of a magnetic recording medium in order to increase the recording density among the performance of a recording head. In order to achieve this, it is necessary to realize a recording head with a narrow track structure in which the width of a bottom pole and a top pole sandwiching a write gap on the air bearing surface is reduced to the order of some microns to submicron. Semiconductor processing technology is used to achieve the narrow track structure.
Now, an example of a method of manufacturing the composite thin film magnetic head will be described as an example of a method of manufacturing the thin film magnetic head of the related art with reference to FIG. 30 to FIG. 35.
In the manufacturing method, as shown in FIG. 30, an insulating layer 102 about 5 to 10 μm thick made of alumina (aluminum oxide, Al2O3), for example, is deposited on a substrate 101 made of altic (Al2O3 and TiC), for example. Then, a bottom shield layer 103 for a reproducing head is formed on the insulating layer 102. Next, for example, alumina about 100 to 200 nm thick is deposited on the bottom shield layer 103, whereby a shield gap film 104 is formed. Next, an MR film 105 of a few tens of nanometers in thickness for making up the MR element for reproducing is formed on the shield gap film 104, and is patterned to a desired shape by photolithography with high precision. Next, a lead layer (not shown in figure) as a lead electrode layer which is electrically connected to the MR film 105 is formed on both sides of the MR film 105. Then, a shield gap film 106 is formed on the lead layer, the shield gap film 104 and the MR film 105, and the MR film 105 is buried in the shield gap films 104 and 106. Next, a top shield-cum-bottom pole (referred to as a bottom pole in the followings) 107 made of permalloy (NiFe), for example, which is a magnetic material used for both the reproducing head and the recording head, is formed on the shield gap film 106.
Next, as shown in FIG. 31, a write gap layer 108 made of an insulating film such as an alumina film is formed on the bottom pole 107, and a photoresist film 109 is formed in a predetermined pattern on the write gap layer 108 by photolithography with high precision. Then, a first layer of a thin film coil 110 for an inductive recording head made of copper (Cu), for example, is formed on the photoresist film 109 by plating, for example. Next, a photoresist film 111 is formed in a predetermined pattern so as to cover the photoresist film 109 and the coil 110 by photolithography with high precision. A heat treatment at 250° C., for example, is applied in order to flatten the photoresist film 111 and to isolate between the turns of the coil 110. Then, a second layer of a thin film coil 112 made of copper, for example, is formed on the photoresist film 111 by plating, for example. Next, a photoresist film 113 is formed in a predetermined pattern on the photoresist film 111 and the coil 112 by photolithography with high precision, and a heat treatment at 250° C., for example, is applied in order to flatten the photoresist film 113 and to isolate between the turns of the coil 112.
Next, as shown in FIG. 32, an opening 108a for forming a magnetic path is formed in a rear position (right-hand side in FIG. 32) of the coils 110 and 112 by partially etching the write gap layer 108. Then, a top yoke-cum-top pole (referred to as a top pole in the followings) 114 made of a magnetic material for a recording head such as permalloy is selectively formed on the write gap layer 108, the photoresist films 109, 111 and 113. The top pole 114 is in contact with the bottom pole 107 in the above-mentioned opening 108a and is magnetically coupled to each other. Next, after etching the write gap layer 108 and the bottom pole 107 about 0.5 μm thick by ion milling using the top pole 114 as a mask, an overcoat layer 115 made of alumina, for example, is formed on the top pole 114. A thin film magnetic head is completed after performing machine processing on the slider to form a track surface of a recording head and a reproducing head, that is, an air bearing surface 120.
FIG. 33 to FIG. 35 show a completed structure of a thin film magnetic head. FIG. 33 shows a cross section of the thin film magnetic head vertical to the air bearing surface 120, while FIG. 34 shows an enlarged cross section of the magnetic pole portion parallel to the air bearing surface 120, and FIG. 35 shows a plan view. FIG. 32 corresponds to a cross-sectional view taken along the line XXX II—XXX II of FIG. 35. In FIG. 33 to FIG. 35, the overcoat layer 115 is omitted.
In order to improve the performance of a thin film magnetic head, it is important to precisely form the throat height TH, an apex angle θ, a pole width P2W and a pole length P2L shown in FIG. 33 and FIG. 34. The apex angle θ is an angle between a line connecting the corners of the side surfaces of the photoresist films 109, 111, 113 on the track surface side and the upper surface of the top pole 114. The pole width P2W determines a write track width of the recording medium. The pole length P2L represents the thickness of the magnetic pole. In FIG. 33 and FIG. 35, “TH0 position” is the position of the edge of the photoresist film 109 on the air bearing surface 120 side, which is an insulating layer for electrically isolating the thin film coils 110 and 112, and represents a reference position when the throat height TH is determined.
As shown in FIG. 34, a structure in which sidewalls of the top pole 114, the write gap layer 108 and part of the bottom pole 107 are vertically formed in a self-aligned manner is called a trim structure. With the trim structure, increase of an effective track width caused by a spread of the magnetic flux occurred while writing on the narrow track can be suppressed. As shown in FIG. 34, a lead layer 121 as a lead electrode layer, which is electrically connected to the MR film 105, is provided on both sides of the MR film 105. The lead layer 121 is omitted in FIG. 30 to FIG. 33.
FIG. 36 shows a plan structure of the top pole 114. As shown in FIG. 36, the top pole 114 comprises a yoke 114a, which makes up most of the top pole 114, and a pole tip 114b with almost a constant width W100 as the pole width P2W. In the connection between the yoke 114a and the pole tip 114b, the outer edge of the yoke 114a forms an angle α with the surface parallel to the air bearing surface 120, while the outer edge of the pole tip 114b forms an angle β with the surface parallel to the air bearing surface 120. α is about 45° degrees, for example, and β is 90° degrees. The width of the pole tip 114b determines the write track width of the recording medium. A portion F is the front side of the TH0 position (close to the air bearing surface 120) of the pole tip 114b and a portion R is the rear side of the TH0 position (close to the yoke 114a) of the pole tip 114b. As shown in FIG. 33, the portion F is extended on the flat write gap layer 108, and the portion R and the yoke 114a are extended on a coil portion (called as an apex portion in the followings) which is covered with the photoresist films 109, 111, and 113 and is protruded like a mountain.
The distinctive shape of the top pole is disclosed in Japanese Patent Application laid-open No. Hei 8-249614, for example.
It is necessary to precisely form the pole width P2W in order to determine the write track width of the recording head. Especially in recent years, in order to attain high surface recording density, that is, to form the recording head with a narrow track structure, microfabrication in which the pole width P2W of the top pole is formed equal to or less than 1.0 μm is required.
As a method of forming the top pole, for example, frame plating method is used as disclosed in Japanese Patent Application laid-open No. Hei 7-262519. When the top pole 114 is formed by the frame plating method, first, a thin electrode film made of permalloy, for example, is formed all over the apex area by sputtering, for example. Next, a photoresist film is formed thereon by applying photoresist, and the photoresist film is patterned in a desired shape through photolithography in order to form a photoresist pattern to be a frame for forming a top pole by plating. The top pole 114 is formed by plating with the electrode film formed earlier being a seed layer and the photoresist pattern being a mask.
There is, for example, 7 to 10 μm or more difference in height between the apex area and other areas. On the apex area, a photoresist of 3 to 4 μm thick is applied. If the film thickness of the photoresist formed on the apex area is required to be 3 μm or more, a photoresist film about 8 to 10 μm thick or more, for example, is formed in the lower part of the apex area since the photoresist with liquidity gathers into a lower area.
In order to form the narrow track as described, it is necessary to form a frame pattern with a width of about 1.0 μm using a photoresist film. That is, a micro pattern with a width of 1.0 μm or less is to be formed by the photoresist film of 8 to 10 μm or thicker. However, it is extremely difficult in a manufacturing process to form such a thick photoresist pattern with a narrow pattern width.
In addition, during an exposure of photolithography, a light for the exposure reflects by an undercoat electrode film as a seed layer and the photoresist film is exposed also by the reflecting light causing deformation of the photoresist pattern and the like. As a result, a photoresist pattern with a sharp and precise pattern shape can not be attained. Therefore, the side walls of the top pole take a round shape so that the top pole can not be formed in a desired shape. Especially, as shown in FIG. 37, it is further difficult to attain a desired width W100A by further microfabricating the pole width P2W. It is because the reflecting light reflected by the undercoat electrode film in the area R of the pole chip portion 114b extended on the apex area includes not only the reflecting light in a vertical direction but also the reflecting light from the slope of the apex area in an oblique direction or in a lateral direction influencing the exposure of the photoresist film. As a result, the pattern width of the photoresist pattern which determines the pole width P2W becomes greater than the anticipated value (as shown by the broken line) and it takes a shape as shown by a solid line in FIG. 37. The width of the portion F of the pole tip 114b which is front of TH0 position (air bearing surface 120 side) is an extremely important factor for determining the track width on the recording medium. Therefore, if the width of the portion F becomes greater than the above-mentioned value W100A, the targeted minute track width can not be attained.
Such problems also exist in the above-mentioned magnetic head disclosed in Japanese Patent laid-open No. Hei 8-249614. It is because, in this magnetic head, the width of the portion which is front of the TH0 position (air bearing surface 120 side) can not be precisely controlled because of the influence on the exposure of the photoresist film by a reflecting light from the apex area in an oblique direction and a lateral direction since the pole width moderately changes from the TH0 position towards the yoke.
As shown in FIG. 37, the portion R of the pole tip 114b, which extends from the TH0 position to the connection between the pole tip 114b and the yoke 114a, has about the same width as the portion F which extends from the TH0 position to the air bearing surface 120, and the portion R has a smaller cross-sectional area. As a result, the magnetic flux from the yoke 114a is saturated in the portion R and can not sufficiently reach the portion F which determines the track width. Therefore, the overwrite performance, that is, the characteristic of overwriting data on a recording medium on which data has already been written, is reduced to a degree about 10 to 20 dB, for example, so that a sufficient overwrite performance can not be attained.